This citizen journalism image shows Syrians inspecting the rubble of damaged buildings due to government airstrikes, in Qusayr, Homs province, Syria, Saturday. The town of Qusayr has been besieged for weeks by regime troops and pro-government gunmen backed by the Lebanese militant Hezbollah group.

Funnels of dirty gray smoke erupted silently from the center of Qusayr, followed seconds later by the ground-shaking thump of exploding artillery shells as the Syrian Army and Hezbollah pressed on today with a grueling offensive to capture the strategic Syrian rebel-held town.

From Lebanon's northern border in the Bekaa Valley, five miles to the south, Qusayr appeared in the dusty haze as a thin slash of white buildings amid a landscape of green orchards and fields. But the bucolic rural scene belies a bloody battle underway for Qusayr, with some 2,000 Syrian rebel fighters and as many as 30,000 civilians hunkered down in the ruins of the town, surrounded by a cordon of elite Syrian Army troops and battle-hardened fighters from the Lebanese Shiite militant group Hezbollah.

"If Qusayr is captured by the Syrian army then the war will be 70 percent over," says Abu Ali, a local businessman and Hezbollah supporter from the Shiite Lebanese town of Hermel, eight miles south of the border.

Although an exaggeration, Abu Ali's assertion illustrates the strategic significance of Qusayr. The town lies between Lebanon's northern border and Homs, Syria's third largest city and adjacent to the key highway linking the capital Damascus to the Mediterranean Coast port of Tartous.

The Syrian armed opposition took over Qusayr in February 2012, turning the town into an important transit point for arms and militants flowing from Lebanon to Homs, as well as a base from which to undermine regime control of the highway.

In recent weeks, President Bashar al-Assad's regime has focused on retaking Qusayr and strengthening its grip on the corridor linking Damascus to Tartous and the adjacent coastal mountains that are home to Syria's Alawite community, the Shiite splinter sect that forms the backbone of the Assad regime.

Syrian Army troops backed by Hezbollah fighters pushed eastward from a string of villages that, although located just inside Syria, are populated by Lebanese Shiites. Fierce battles broke out as the regime forces accompanied by Hezbollah fighters gradually seized a number of small villages populated mainly by Sunni supporters of the opposition. Retreating rebel forces struck back by firing Katyusha rockets at Shiite-populated Hezbollah strongholds in Lebanon's northern Bekaa Valley.

By last week, the Syrian Army and Hezbollah had also seized some villages to the north of Qusayr, effectively surrounding the town.

"We blocked all the area around Qusayr to stop trouble coming to Lebanon," says Abu Khalil, a veteran Hezbollah fighter, justifying the militant Shiite group's assistance to Syrian troops.

Coming out into the open

Hezbollah's presence in Syria has steadily grown over the past year. Its leadership initially denied dispatching fighters into Syria to assist the Assad regime, but it has become impossible to hide its assistance as the number of fighters killed or wounded in action rises, nor stop the fervent chatter within Shiite circles in Lebanon.

"It is legitimate for Hezbollah to be fighting in Qusayr because they are still defending us here in Lebanon," says Rakkan Jafaar, the mayor of Sahlet al-My, a small village on the border beside Qasr. "The people in Qusayr used to joke about how they would come here and take our homes. If Qusayr is taken, the situation should improve for us here."

Syrian opposition sources claimed that more than 20 Hezbollah men were killed yesterday and more than 60 were wounded. Rebel fighters in touch with comrades on the ground in Qusayr insisted the number was even higher.

"We ambushed a Hezbollah unit on the edge of Qusayr and killed 40 of them and many more were wounded. We chopped them to pieces," says Abu Omar, a Lebanese Sunni volunteer fighter with the rebel Farouq Brigade, laughing as he made chopping motions with his hand.

He added that, having had a year to prepare, the rebel forces in Qusayr – a mix of local "brigades" all fighting under the banner of the powerful Farouq Brigade – were confident that they could hold out against the Syrian Army and Hezbollah. Hezbollah and rebel sources both say that defensive tunnel networks have been dug and numerous booby traps prepared in Qusayr.

"Qusayr will never fall. We are a very strong force," Abu Omar says.

He says that the rebels seized a substantial number of weapons from an air base just north of Qusayr that was overrun a few weeks ago. Today, thick clouds of black smoke billowed from the direction of that air base as Syrian troops fought to retake the facility.

Hezbollah funerals

There was little disguising the state of tension and activity in the northern Bekaa Valley Monday as the fighting raged a few miles to the north. At Maqneh, a Shiite village on the main highway running from Baalbek in the central Bekaa to the border, Hezbollah men had partially blocked the road with concrete blocks festooned with yellow party flags. A combatant in a full camouflage uniform, tan military boots, and a pair of sunglasses guided traffic along a detour. From further up the road came the sound of drums and a brass band, followed minutes later by the crackle of automatic rifle fire indicating that a funeral for a slain militant was underway.

A few miles north of Maqneh, at Rasm al-Hadeth, another funeral was being held. One fighter stood on the side of the road, a rifle slung around his neck as others directed traffic. In the late afternoon, Hezbollah vehicles – SUVs with tinted windows and no number plates – gathered at a junction in Baalbek. Men jumping out, brandishing AK-47 rifles. Shortly afterward, bursts of machine gun fire echoed across the town and its magnificent Roman temples as yet another fighter was laid to rest.

Closer to the border, ambulances, lights flashing and sirens blaring, weaved through traffic and potholes while flanked front and back by more Hezbollah vehicles.

The battle in Qusayr is Hezbollah's first major combat action since the end of the month-long war against Israel in 2006. Although the organization is dedicated to the confrontation against Israel, its cadres are now in Syria battling fellow Arab Muslims, albeit Sunnis. Meanwhile, Israeli jets penetrate Lebanese airspace on a daily basis. Two weeks ago they bombed suspected Hezbollah arms stockpiles outside Damascus in two separate sorties. Neither Hezbollah nor regime forces retaliated.

Syria is the linchpin connecting Hezbollah by land to its patron Iran, serving as a conduit for the flow of arms and granting the Shiite group strategic depth. The collapse of the Assad regime would represent a serious blow to Iran and Hezbollah, leaving them isolated on opposite ends of the Middle East.

Hezbollah's rapidly expanding role in Syria is regarded as part of a strategic decision undertaken by the party, Damascus, and Tehran to safeguard the Assad regime at all costs. To soothe any misgivings among Hezbollah's rank and file, the party's leadership has crafted a narrative that the West and Israel are using militant Sunni jihadists to oust the Assad regime and weaken the "resistance front" of Iran, Syria, and Hezbollah for the benefit of the Jewish state.

It is a rationale that has been absorbed by the Hezbollah combatants. Asked how he felt to be fighting Arab Muslims today, having not fought Israeli troops for nearly seven years, Abu Khalil shook his head.

"No, we are fighting Israelis in Syria," he says. "Only they are wearing a dishdash and carrying the Quran. But it is the same Western and Israeli project that wants to weaken the resistance."